1. Common Ion Effect
Buffers

2. Common Ion Effect
Sometimes the equilibrium solutions have 2 ions in common
For example if I mixed HF & NaF
The main reaction is HF  H+ + F-

3. Common Ion Effect Which way will the reaction shift if NaF is added?
What effect will this have on pH?

4. Example
What is the pH of a 0.10M solution of HC2H3O2 (Ka = 1.8 x10-5)

5. Example
HC2H3O2  H+ + C2H3O Ka = 1.8 x 10-5 I C E

6. Example
A mixture contains 0.10M HC2H3O2 (Ka = 1.8 x10-5) & 0.10 M NaC2H3O2. Calculate the pH.

7. Example
HC2H3O2  H+ + C2H3O Ka = 1.8 x 10-5 I C E

8. What are buffers? Buffers resist changes in pH They must have 2 parts…
Weak acid & a conjugate base OR
Weak base & a conjugate acid
The concentrations of the 2 MUST be with in a factor of 10!!!

9. Buffers
[NaC2H3O2 ]
[HC2H3O2 ]
Buffer?
0.10M
1.0M
0.01M

10. Example
What is the pH of a solution containing 50. mL of 0.50M NaC2H3O2 & 25 mL of 0.25M HC2H3O2. (Ka = 1.8 x10-5).

11. Example
HC2H3O2  H+ + C2H3O Ka = 1.8 x 10-5 I C E

12. Henderson Hasselbach Equation
Really easy equation to use ONLY with buffer solutions!!!
pH = pKa + log [B]/[A]

13. The last example using HH
pH = pKa + log [B]/[A]

14. Example (ICE TABLE)
What is the pH of a solution containing 25 mL of 0.150MHClO & 32mL of 0.45M KClO. Ka = 3.5x10-8

15. Example (ICE TABLE)
HClO H ClO Ka = 3.5x10-8 I C E

16. Example (HH)
pH = pKa + log [B]/[A]

17. Example (ICE TABLE)
What is the pH of a solution containing 25 mL of 0.50M CH3NH3NO3 is mixed with 75 mL of 0.30 M CH3NH2 (Kb CH3NH2 = 4.38 x10-4)

18. Example (ICE TABLE)
CH3NH2 + H2O  CH3NH OH Ka = 4.38x10-4 I C E

19. Example
Calculate the mass of NaF that must be added to ml of 0.50M HF to form a solution with a pH of Ka = 7.2x10-4

20. Example (ICE TABLE)
HF  H F Ka = 7.2x10-4 I C E